Unread mail count

I have deleted emails on my blackberry phone, but they are showing as unread on my ipad yahoo mail, it's driving me nuts as I can't find the unread messages yet the little red icon says I now have 21 unread! In the inbox there are only 3 emails all of which are read!, I have checked all mail boxes I.e. Junk, trash etc and there are no unread emails in there! Somebody please help me